This invention is directed in general to back lit signs that are illuminated using light fiber(s) and that exhibit diffuse reflection of light from the light fiber(s). More particularly, the invention is directed to such a lighted sign that is compact in the thickness dimension (i.e., has a shallow depth) and requires little maintenance. Even more particularly, the invention is directed to such a lighted sign that is suitable for use on a vehicle (e.g., an automobile). The invention is also directed to methods for making and using these signs.
Lighted signs are everywhere in modern countries. The sign can educate, entertain, inform, or warn the viewer. The sign can be designed for close or distant viewing. Lighting is provided to assure the viewer can see the message, particularly during dimly lit days or nighttime. Lights require energy to power them. Modern countries readily can provide the power, but those who pay for the energy are always seeking more efficient delivery of the power and more efficient usage of the power. The energy required to power a lighted sign should not be wasted, for economic and environmental reasons. Lighted signs can be xe2x80x9cfront litxe2x80x9d or xe2x80x9cback litxe2x80x9d. The former typically include such signs as billboards or other displays where the light is shone from the perimeter of the sign at an angle toward the sign. The latter typically have a translucent surface through which the light is seen and on which the message or image is placed. Uniformity of light emanating from the translucent surface is important. Often, the translucent surface includes some element that diffuses the light to reduce the identification by the viewer of the point or linear source of the light within the sign housing. Typical back lit sign faces today are between 20% to 40% transmissive, emphasizing the importance of highly reflective sign cavities. White paint has been used to make the inside cavity surfaces of such signs reflective.
Lighted signs have been made in many configurations with a variety of light sources. Lighted signs have been integral to or mounted as a fixture on a building or vehicle, freestanding, or a part of other apparatus or equipment. Whenever the sign is lighted, the power used should not be wasted. Lighted signs have bad many geometric configurations. Lighted signs that have a perimeter shape of a complex geometry to convey the intended message are entirely different types of signs from lighted signs that rely on a Euclidean geometry with the intended message within the perimeter. In the industry, an example of the former type of sign is called xe2x80x9cchannel lettersxe2x80x9d and can generically be called xe2x80x9ccomplex shape lighted signs.xe2x80x9d The latter are called xe2x80x9csign cabinetsxe2x80x9d because the perimeter of the sign is irrelevant to the message being conveyed. Nonlimiting examples of sign cabinets include rectangular, oval, circular, elliptical, and other Euclidean geometrical shapes. Nonlimiting examples of complex shape lighted signs include letters, profiles, silhouettes, characters, or any other shape desired by a customer that helps to advertise, educate, warn or the like.
In one particular application, sign cabinet type illuminated signs, back lit with fluorescent lighting, have been mounted on tractor trailer trucks in the front of the truck cab, above the windshield or windscreen. Such signs typically have a depth of 30 cm (12 in.) or more, with widths of about 2 m (6.5 ft.) and heights of about 50 cm (20 in.). Interior cabin space within the cab of such trucks, as with most vehicles, is limited. Therefore, it is desirable to utilize this space in the most efficient manner possible. However, because of their depth (e.g., 30 cm or more), too much valuable interior cabin space has had to be used to accommodate such illuminated signs. Another problem with such prior truck signs is associated with maintaining them. The cabinet portion of these truck signs has typically been made integral with the cab body of the truck. In addition, in order to protect the florescent bulbs and ballast inside the back lit truck sign from the weather, the face of the sign is typically sealed in place, for example, with a rubber ring gasket. As a result, the replacement of burned-out bulbs or worn-out ballast is a time consuming and costly procedure.
Therefore, there is a need for a more compact, particularly in the thickness dimension (i.e., depth) and low maintenance illuminated sign using light fiber(s) and that exhibit diffuse reflection of light from the light fiber(s). More particularly, the invention is directed to such a lighted sign that is compact in the thickness dimension (i.e., has a shallow depth) and requires little maintenance. Even more particularly, the invention is directed to such a lighted sign that is suitable for use on a vehicle (e.g., an automobile).
What the art of lighted signs needs is a more compact, particularly in the thickness dimension (i.e., return depth), and low maintenance back lit illuminated sign, especially a back lit sign suitable for use on a vehicle (e.g., an automobile, bus, truck, train, airplane, watercraft and aircraft).
One aspect of the invention is a shallow back lit illuminated sign comprising a housing, a light source and at least one side-light emitting fiber. The housing has a sign face and an interior surface that includes a back surface. The sign face has an illuminated area (i.e., an area of the sign face that will be illuminated) through which light from inside the housing can be diffusely transmitted out of the housing. At least a portion, and preferably most, if not all, of the interior surface is diffuse reflective enough to provide luminance uniformity to the sign. Preferably, the interior surface is sufficiently diffuse reflective to also provide luminous efficiency (i.e., ratio of the amount of light transmitted out of the sign to the amount of light emitted from the fiber(s)) to the sign. The back surface is located at a depth from the sign face, and the sign has a large aspect ratio.
The light source is suitable for supplying light to a light fiber. It is desirable for the light source to be located outside of the housing, but not so far from the housing as to result in an objectionable loss in the efficiency of the fiber (i.e., requiring significantly more power to operate properly). One or more side-light emitting fibers are connected so as to receive light from the light source and are mounted within the housing so as to significantly limit the amount of emitted light, from the fiber(s), that travels directly to the sign face (i.e., that does not reflect at least once off of a diffuse reflective surface before traveling to the sign face). These fibers can be the rigid or flexible type.
The amount of emitted light that travels directly to the sign face is considered significantly limited when there are no visually apparent (with normal contrast sensitivity) and undesirable or offensive xe2x80x9chot spotsxe2x80x9d on the sign face. To help prevent such direct travel of the emitted light to the sign face, it is desirable for the side-light fiber(s) to be located on the interior surface of the housing, with the light being emitted from the fiber(s) at a narrow enough angular distribution (e.g., 5-20 degrees) that the emitted light travels in a direction generally parallel to the sign face, while allowing incidence on the back surface and other portions of the interior surface.
The diffuse reflective portion of the interior surface is, preferably, a film or sheet attached to the inside of the housing such as, for example, by an adhesive. It can also be desirable for the back surface to be diffuse reflective and have a concave curvature relative to the sign face. The sign is preferably a sign cabinet and can have a housing that is mountable on a vehicle.
A sign face that xe2x80x9cdiffusely transmits lightxe2x80x9d is one that scatters transmitted light and, preferably, is one that exhibits an appropriate balance between light transmission and reflection, with a low absorption of light, in order to provide the sign face with the brightness and degree of luminance uniformity desired.
A large xe2x80x9caspect ratioxe2x80x9d is where the illuminated area of the sign face is large relative to the distance or depth between the sign face and the back surface. Typically, the depth is substantially smaller then the major dimensions of the housing.
xe2x80x9cFilmxe2x80x9d means a thin, flexible sheet in existence prior to contact with the sign housing.
A xe2x80x9cdiffuse reflectivexe2x80x9d surface means a surface that is reflective without being a mirrored surface (i.e., a specular reflector). xe2x80x9cReflectivexe2x80x9d is an adjective of the noun xe2x80x9cReflectivityxe2x80x9d which is expressed in an industrial standard established by the American Society for the Testing of Materials (ASTM) in Standard ASTM E1164-94.
xe2x80x9cLuminance uniformityxe2x80x9d means that the brightness of light emanating from a translucent surface is substantially uniform in a large number of locations on the surface, yielding a sign that does not significantly identify the location(s) of light source(s) within the sign housing.
xe2x80x9cHot spotsxe2x80x9d are areas on the sign face of noticeably higher brightness, typically the result of unreflected and undiffused light traveling directly to the sign face.
In another aspect of the invention, a vehicle is provided that comprise the above sign. The vehicle can be an automobile such as, for example, a truck. It can be desirable for the vehicle to be a truck that has a cab with an exterior surface and an interior cabin space, when the sign has a depth and is mounted in the cab such that the sign face is about flush with the exterior surface and the housing extends very little, if any, into the interior cabin space. The boundary of the interior cabin is typically defined, at least in part, by a headliner. It is desirable for the back of the housing not to extend beyond the headliner. Preferably, the housing is dimensioned to fit between the exterior of the truck cab and the headliner.
The inventive sign, for use in a vehicle, is energy efficient and does not require a power supply separate from the vehicle""s conventional power generation system (e.g., the battery). The invention can also be made environmentally friendly. There are no disposal issues like those with fluorescent light systems, which can contain, e.g., heavy metals, like the mercury in some fluorescent lights.
In an additional aspect of the invention an unassembled shallow back lit illuminated sign is provided. The unassembled sign comprises a sign face panel and at least one interior surface panel which can be assembled to form a housing, a light source for supplying light to a light fiber, and at least one side-light emitting fiber. The sign face panel has an illuminated area that diffusely transmits light, and at least one interior surface panel which can be assembled to form a housing. The interior surface of the housing can be a shaped single panel or multiple panels which can be assembled. The sign can also be provided in a unitary (e.g., sealed) structure, as well as in multiple pieces. When assembled to form the housing, the interior surface panel(s) form an interior surface of the housing including a back surface, the interior surface has at least a portion thereof that is diffuse reflective enough to provide luminance uniformity to the assembled sign, the back surface is located at a depth from the sign face, and the illuminated area is large relative to the depth. The side-light emitting fiber is connectable so as to receive light from the light source and mountable within the assembled housing so as to significantly limit the amount of emitted light, from the fiber, that travels directly to the sign face.
The diffuse reflectivity of the interior surface can be provided by at least one diffuse reflective film either pre-attached to or separate from but attachable to the at least one interior surface panel. In addition, the at least one interior surface panel can be a plurality of interior surface panels and the diffuse reflectivity of the interior surface can be provided by a plurality of diffuse reflective films, with each film being either pre-attached to or separate from but attachable to at least one of the interior surface panels.
It can be desirable for a plurality of interior surface panels to be used, and the back surface to be formed by at least two interior surface panels.
In a further aspect of the invention, the unassembled sign is provided in the form of a packaged kit.
The diffuse reflective portion(s) of an interior surface of the housing captures the lumens of light from the light source or those lumens of light reflecting back from a diffusing panel or sides and backs of the housing (e.g., a light cabinet) and re-directs such light toward the viewer, thereby providing luminance uniformity on the translucent surface of the sign face.
It is desirable for the diffuse reflectivity of the overall interior surface to be at least 80%, preferably at least about 90%, more preferably at least about 92% and even more preferably at least about 94%, as measured using ASTM E1164-94 at a wavelength of 550 nm.
The reflectivity of the film can be controlled to provide desired power consumption reductions, as well as improved luminance uniformity, according to the needs of those skilled in the art of signage construction. An improvement in luminance uniformity can also provide significant power reduction for a sign. Thus, both the utility and aesthetics of a sign can be addressed by the invention.